YJIT: Avoid leaks by skipping objects with a singleton class

[XrXr]

For receiver with a singleton class, there are multiple vectors YJIT can
end up retaining the object. There is a path in jit_guard_known_klass()
that bakes the receiver into the code, and the object could also be kept
alive indirectly through a path starting at the CME object baked into
the code.

To avoid these leaks, avoid compiling calls on objects with a singleton
class.

See: Shopify#552

There is little to no performance impact on headlining benchmarks:

yjit-pre: ruby 3.4.0dev (2024-01-23T19:00:05Z master 557b69e83b) +YJIT [x86_64-linux]
yjit-post: ruby 3.4.0dev (2024-01-23T23:05:17Z yjit-stop-singleto.. ab19268644) +YJIT [x86_64-linux]

--------------  -------------  ----------  --------------  ----------  -----------------  ------------------
bench           yjit-pre (ms)  stddev (%)  yjit-post (ms)  stddev (%)  yjit-post 1st itr  yjit-pre/yjit-post
activerecord    41.3           1.2         41.0            1.1         1.02               1.01              
chunky-png      627.4          0.5         637.1           0.7         0.99               0.98              
erubi-rails     1397.3         0.4         1439.6          0.4         0.97               0.97              
hexapdf         2112.7         1.9         2117.5          1.3         0.99               1.00              
liquid-c        56.8           1.4         57.1            1.4         1.00               1.00              
liquid-compile  57.3           2.0         57.3            1.5         1.00               1.00              
liquid-render   78.4           1.1         78.7            1.2         1.00               1.00              
lobsters        855.4          1.4         862.8           1.1         1.00               0.99              
mail            120.7          0.8         120.9           0.8         1.00               1.00              
psych-load      1807.1         0.1         1798.4          0.1         1.00               1.00              
railsbench      1726.0         0.3         1735.3          0.3         1.00               0.99              
rubocop         116.6          5.0         116.1           5.2         0.99               1.00              
ruby-lsp        116.8          3.6         114.7           3.5         0.97               1.02              
sequel          66.3           0.8         66.3            0.8         1.00               1.00              
--------------  -------------  ----------  --------------  ----------  -----------------  ------------------